PROVIDED. Spinal manipulation is a popular and widely used CAM treatment for back pain. It has been shown to be effective in a preponderance of clinical trials, but the reasons why manipulation works are unknown. The long-term goal for this study is to understand the physiological mechanisms of various forms of spinal manipulation in order to refine and improve this therapy for appropriately selected patients. Back pain patients demonstrate deficiencies in sensorimotor function. These may be related to the effects that manipulation appears to have on neurophysiology. Hence, the objective of this study is to assess the effects of high-velocity low-amplitude spinal manipulation(HVLA-SM) and low-velocity variable amplitude spinal manipulation (LVVA-SM) on three types of sensorimotor abilities in patients with low back pain. In collaboration with the University of Iowa, the Palmer Center for Chiropractic Research will pursue the following Specific Aims: 1) To determine the immediate pre-to-post changes from HVLA-SM and LVVA-SM, compared to a no-treatment control, on sensorimotor function as measured by: lumbo-pelvic repositioning ability, standing postural sway, and response to sudden trunk loading; 2) To determine the effects of 2 weeks (4 applications @ 2 per week) of HVLA-SM and LVVA-SM, compared to a no-treatment control, on sensorimotor function as measured by: lumbo-pelvic repositioning ability, standing postural sway, and response to sudden trunk loading; 3) To determine the effects of 6 weeks (12 applications @ 2 per week) of HVLA-SM and LVVA-SM on sensorimotor function as measured by: lumbo-pelvic repositioning ability, standing postural sway, and response to sudden trunk loading; 4) To explore whether changes in sensorimotor function are associated with changes in self-reported back pain intensity, related disability, or health status at 2 weeks (after 4 SM Visits) and at 6 weeks (after 12 SM Visits); and 5) To determine if sensorimotor function changes are greater in patients clinically classified as being most appropriate for manipulation. If spinal manipulation is demontrated to improve the sensorimotor functions of back pain patients and correlate with improvements in clinical symptoms and related disability, it will further define the appropriate clinical role of this CAM treatment, potentially enhance understanding about the etiology of back pain, and lead to improved treatment for a costly and common public health problem.